1. Field of the Invention
The present invention relates to the field of butt resistance welding and, more particularly, to a flash-butt resistance welding process.
The invention can be used to advantage for welding thick-walled or large compact parts on machines for flash-butt resistance welding.
2. Description of the Prior Art
Known in the prior art is a flash-butt resistance welding process (UK Pat. No. 984,296, Cl. B23K, 1965) with a preheating cycle in which the parts are heated at the initial welding stage, using a resistance method. The parts are preheated by periodic short-time current pulse. The current is interrupted either by opening of the welding circuit by reciprocating motion of one of the parts, or by periodic disconnection of the welding transformer primary winding from the mains. The parts are periodically drawn together to form a steady contact between their touching surfaces and then they are drawn apart to open the welding circuit.
However, the known process fails to ensure uniform heating of parts across their section, hence it fails to ensure high quality of the welded joint.
Also known in the prior art is a flash welding process without preheating (USSR Inventor's Certificate No. 226,745 IPC H05B, publ. 1968) which ensures a high quality of the welded joint. In this process the converging speed of the welded parts is periodically and momentarily raised. With a sharply raised speed the number of elementary contacts arising between the surfaces of the welded parts increases greatly and after a decrease of this speed the number of concurrently existing contacts remains the same within a certain time. The speed changes are regulated so that after the current (voltage, power) is increased to a certain limit, the speed begins to be reduced to the initial value which rules out the short circuit between the butts of the parts. However, during the reduction of speed it becomes practically impossible to avoid opening of the welding circuit which brings about pauses in the process of flashing. This calls for increasing the welding time and this reduces the output.